The present invention is directed generally to an apparatus and method for increasing the hydraulic capacity of a sewer system. More particularly, the present invention is directed to a receiving structure positioned within or proximate to an existing gravity sewer system for increasing the hydraulic capacity of the sewer system during a period in which the capacity of the existing sewer system would otherwise be exceeded.
Combined sewer systems were the “state-of-the-art” during the early 20th century. In addition to the collection and transport of municipal wastewater, these combined sewers were designed for stormwater flows as well—therefore the term “combined.” The design of combined sewer systems included “overflow structures.” When a wet weather event (for example, a storm, heavy rain or snowmelt) created stormwater flows which exceeded the design capacity (i.e., hydraulic capacity) of the combined sewer system, the excess flow (i.e., the combined sewer overflow “CSO”) would be intentionally diverted to nearby surface water via these overflow structures.
Later in the 20th century, the “state-of-the-art” shifted to the design and construction of separate sewers—individual sewer systems for municipal wastewater and stormwater. The design capacity of the sanitary sewer was intended to collect and transport municipal wastewater from the service area. Experience has shown that unintended water from non-municipal sources (i.e., stormwater) also enters the sanitary sewers. During wet weather events these excessive flows create sanitary sewer overflows (“SSO”) at locations which were not intentionally designed to accommodate such overflows.
One example of a prior art sewer system is shown in FIG. 1. The prior art sewer system, generally designated 12, typically includes an upstream portion, pipe or conduit 12a and a downstream portion, pipe or conduit 12b. The downstream conduit 12b typically has an existing capacity (due to size, slope, etc.) which is greater than the increased capacity desired for the upstream conduit 12a. The downstream conduit 12b is typically connected to or leads to a treatment facility (not shown). The upstream and downstream conduits 12a, 12b may be operatively connected by a manhole or other open area 40 having a removable manhole cover or lid 42 to provide access to the manhole 40.
At full-flow of a liquid, such as wastewater, stormwater, or a combination of wastewater and stormwater, a hydraulic gradient 14 is typically parallel to the slope of the upstream conduit 12a. While normally depicted above the upstream conduit 12a, in FIG. 1 the hydraulic gradient 14 is intentionally shown beneath the upstream conduit 12a in order to more clearly demonstrate the effect of the present invention. The upstream and downstream conduits 12a, 12b have a certain hydraulic capacity at full-flow of a liquid, which is determined by its size, shape and/or material-of-construction and its hydraulic gradient 14. Upstream flows (i.e., to the left in FIG. 1) in excess of this full-flow hydraulic capacity will cause the liquid in the upstream conduit 12a to back-up and overflow.
The current approach taken by the United States Environmental Protection Agency (“USEPA”) to deal with the issue of CSO and SSO environmental impacts is based on legally-binding “Consent Decree” agreements between the USEPA and the sewer system entity—typically a municipal government or agency. The individually-negotiated Consent Decrees include a scope-of-work and schedule intended to reduce the frequency and volume of CSO during wet weather events.
The scope-of-work includes an assessment and evaluation of technically-feasible alternatives. Where increased hydraulic capacity is needed in order to reduce the frequency and volume of overflows, the typical alternatives often considered are parallel sewers and/or tunnels. Such alternatives are often very expensive solutions to deal with short-duration problems created by only a few wet weather events annually.
Therefore, it would be desirable to create an apparatus and method that alleviates or overcomes the above-described disadvantages of conventional sewer systems. More specifically, it would be desirable to create an attachment or addition to existing gravity sewer systems that—when necessary or desired—increases the hydraulic capacity of the sewer system, which is preferably an established or existing gravity sewer system. The present invention accomplishes the above objectives.